The Biostatistics Core Facility (BCF) of the University of Chicago Cancer Research Center (UCCRC) provides collaborative statistical support to UCCRC investigators engaged in clinical, basic, and population science research. The Facility is currently staffed by five PhD and two masters-level biostatisticians, in addition to the Scientific and Technical Directors. The services provided by the BCF include collaboration in the formation of study designs and data analysis plans, protocol development and statistical analysis for Phase I, Phase II, and Phase III clinical trials, assistance in the design and analysis of retrospective and prospective observational studies, and statistical collaboration on basic science and animal research projects. Clarification of specific aims and hypotheses to be tested, specification of primary and secondary outcome variables, sample-size (power) calculations, and development of data analysis plans are major areas of activity during the study design phase, followed by statistical analysis and assistance in the preparation of manuscripts for publication after completion of data collection. During the past five years, members of the BCF have co-authored over 80 collaborative publications. The BCF also interacts closely with the Cancer Clinical Trials Office and the Biomedical Informatics Core (a developing UCCRC Core) of the Biological Sciences Division on database development and data management procedures to ensure a high level of data quality for clinical trials and other studies conducted within the UCCRC. The BCF collaborates heavily with UCCRC investigators in the development of new grant applications, ranging from R21 "quick trials" to multi-project SPORE grant submissions. Presently, BCF staff are engaged in active support of over 20 NIH/NCI-funded studies, as well as an industry-sponsored, multicenter, Phase III clinical trial. BCF members also serve on two key UCCRC committees, namely, the Clinical Trials Review Committee and the Scientific and Accrual Monitoring Committee, thereby ensuring that all protocols and cancer-related research projects undergo rigorous biostatistical review and that patient accrual to ongoing studies is adequate. Finally, BCF members participate in teaching activities, and conduct statistical methodological research in support of projects conducted within the UCCRC. Thus, the BCF plays a major role in meeting the scientific needs and objectives of the University of Chicago Cancer Research Center.